A near-distance wireless communication network configured by sensor devices for acquiring biological information and a gateway device for collecting items of biological information from the sensor devices and transmitting the biological information to another network, is called a body area network (BAN) as the case may be. A BAN-utilized scheme enables realization of an application for making a medical check more efficient in a medical institution by constantly-conducting measurements of the biological information such as a heart beat and a body temperature or an application for enriching a health care outside the medical institution.
FIGS. 9 and 10 are diagrams each illustrating an outline of the BAN system. Main items considered as a communication technique for the BAN are a technique (refer to, e.g., Patent document 1 given below) of utilizing, as a propagation channel, a space distanced from a human body as illustrated in FIG. 9 and a technique (refer to, e.g., Patent documents 2 and 3 given below) of utilizing the human body as the propagation channel as illustrated in FIG. 10. Hereinafter, the former technique is termed an aerial communication, while the latter technique is termed a human-body communication. The human-body communication includes a technique of making use of a change of currents in a human body, a technique of utilizing an electric field on the surface of the human body, etc.
An example of the aerial communication shown in FIG. 9 is that respective sensor devices 901, 902 perform wireless communications by use of antennas 903, 904. An example of the human-body communication shown in FIG. 10 is that respective sensor devices 911, 912 perform the wireless communications by use of, e.g., electrodes 913, 914 attached to the human body.
It is general that a frequency zone for use in the BAN system using the aerial communication ranges from several hundred mega hertz (MHz) through several Giga hertz (GHz), and by contrast the BAN system using the human-body communication involves employing a frequency zone equal to or lower than 10 (MHz) corresponding to a characteristic of the propagation channel.    [Patent document 1]: Japanese Patent No. 3708354    [Patent document 2]: Japanese Patent No. 3707463    [Patent document 3]: Japanese Laid-Open Patent Publication No. 2001-144662